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Karst aquifers represent important but very vulnerable sources for water supply to a significant part of the Earth's population. For sustainable use of these resources, development of integrated management tools based on numerical groundwater models is required. In principle karst aquifers are characterized by the presence of two distinct flow domains: the limestone matrix fractures and the conduits. A flow model of karst aquifers requires detailed, spatially distributed information on the hydrologic characteristics of the aquifer and flow paths. Geophysical methods determining the distribution of the electrical resistivities within the subsurface could provide such information. An international scientific research project was initiated to explore the potential of airborne electromagnetic mapping for providing such innovative information for improving groundwater modelling of karst aquifers. The project study area is located in the Sian Ka'an Biosphere Reserve located in Yucatán, Mexico, a coastal wetland of international importance. As a first step ground geoelectric and ground electromagnetic measurements were performed in March 2006 to determine the electrical properties of the Sian Ka'an Biosphere Reserve subsurface environment. These results were used for 3D forward modelling to calculate the expected airborne electromagnetic response. Based on these promising results, an airborne pilot survey was performed in 2007 to evaluate the applicability of airborne electromagnetic methodology. This survey covers an area of 40 square kilometres above the well-mapped Ox Bel Ha cave system. The results showed that the signature of the cave system could be clearly detected. The pilot survey offered as well the chance to define the limits of current state-of-the-art airborne data acquisition and inversion. The study helped to define the needs for further developments and improvements to establish the frequency domain electromagnetic method as a practical karst exploration method.water supply for a significant portion of the Earth's population (e.g., Darnault 2008).In order to protect karstic groundwater systems and associated ecosystems, it is necessary to develop integrated tools for sustainable management of these resources based on accurate coupled surface-/groundwater models. Although the mathematical formulation of such models is well established, results are mostly unsatisfactory. The reason for this is that both location and geometry of dominant karst features, controlling the flow, are either not known at all or not known with the required accu-